Standard booms of backhoes are conventionally integrally formed from a base end side to a distal end side in which the main body portion is composed of left and right side walls and top and bottom walls. In this boom, the base end side is provided with a pivoted coupling member that is curved at a midway point in the lengthwise direction so as to be convex toward the upper side and that is pivotably coupled to the boom support section of the running body. This boom has an arm that is pivotably coupled to the distal end side (see Patent Document 1).
Additionally, an example of a boom whose base end is pivotably coupled to the running body side and whose distal end is pivotably coupled to an arm is a boom (referred to as a two-piece boom) composed of a first boom pivotably coupled to the running body side, and a second boom in which the base end side is pivotably coupled to the distal end side of the first boom so as to be capable of rotation about the lateral axis and in which an arm is pivotably coupled to the distal end side (see Patent Document 2).
Patent Document 1: Japanese Laid-open Patent Application No. 2003-328383
Patent Document 2: Japanese Laid-open Patent Application No. 11-241363